1. Field of the Invention
The present invention relates to a improved blower for use in a variety of OA (office automation) equipment.
2. Description of the Related Art
Each OA equipment houses many electronic circuits within its casing, so that the heat generated by electronic parts constituting those electronic circuits are hard to be discharged. Because of this, there is a fear that some of the electronic parts are broken or deteriorated. Particularly in view of the recent trend towards downsizing of the OA equipment, in which the equipment is simply reduced in size despite the absence of significant reduction in quality of the generated heat, countermeasures against the heat has come to an important technical object. Then troubles that would be caused by heat generated inside is prevented by forming a ventilation hole on a side wall of the equipment and mounting a blower around the hole to discharge the internal heat to the outside of the equipment.
An example of a blower that has been frequently used will now be described with reference to FIG. 3. Reference symbol 1 denotes a tubular casing the inside of which is sloped to form a venturi portion 2. A housing 3 is formed integrally with this casing 1 at the center. A bearing housing 4 is formed on the central portion of the housing. Outer races of bearings 5 and 6 are supported inside the bearing housing 4 and a shaft 7 is fitted and inserted to inner races of the bearings 5 and 6. A ring 8 is mounted at the lower end of the shaft 7 to prevent thereby the shaft 7 from being pulled out and position the shaft 7 in the axial direction.
Reference symbol 9 denotes an impeller made of synthetic resins. This impeller 9 comprises a body 10 having in section a shape of letter C and blades 11 formed around the periphery of the body 10, which are integrally formed. In forming the impeller 9, a ring-shaped motor yoke 12 is insert-molded at the inner circumferential portion of the body 10 and the shaft 7 is insert-molded at the central portion of the body 10. A knurling groove 13 is formed near the top end of the shaft 7 so that the shaft 7 is tightly joined to the body 10 at the time of the insert molding, preventing separation from the body 10 during rotation. A ring-shaped magnet 14 is fixed by adhesives to the inner circumference of the motor yoke 12. These parts together form a rotary part. A ring-shaped spring 15 is interposed between a portion of the body 10 near the shaft 7 and the inner race of the bearing 5, which gives the impeller 9 an upward pressurization in the drawing.
A stator core 17 around which a stator coil 16 is coiled is arranged on the outside of the bearing housing 4 and fixed to the bearing housing 4 to form a stationary part. A PC (printed circuit) board 18 on which electronic circuits as a brushless motor are formed from electronic parts is mounted on a lower portion of the stator core 17. The electronic circuits incorporated into this PC board 18 control current for rotating the rotary part relative to the stationary part. A pin-like connecting terminal 19 is projected downward from the stator core 17 to pierce through a part of the PC board 18, thereby electrically connecting the stator coil 16 to the circuits on the PC board 18. A lead 20 is connected to the PC board 18 for feeding electric power to the PC board 18.
The thus constructed blower is used when mounted around the ventilation hole of the casing of the OA equipment. In the mounting work, the upper side of the blower in the drawing is directed to the outside of the box of the OA equipment with the shaft 7 being directed in the horizontal direction. When a predetermined voltage is fed from a power source to the lead 20 under this condition, the current controlled by a control circuit on the PC board 18 is caused to flow through the stator coil 16 so that the rotary part is rotated by a magnetic interference action between the magnetic flux generated in the stator core 17 and the magnetic flux generated by the magnet 14. The impeller 9 is rotated so that the air in the lower part of the box in the drawing is sucked and is discharged from the venturi portion 2 toward the outside in the upper part in the drawing. With this air flow operation, the interior of the casing is cooled.
The blower with the above structure has no problem when adopted by equipment used in a usual office. However, the PC board in the blower is not completely covered, which makes the blower unsuitable for use under severe circumstances such as construction sites especially in terms of dust-proof and drip/water-proof characteristics.